The shortage and high price of gasoline has recently led to an intensified search for a more efficient automobile. In this regard, the ability to store braking energy in a usable form has shown great promise. One of the best ways for recovering and storing the energy usually lost in the braking mode is in a spinning flywheel. A vehicle equipped with a flywheel energy storage system is thus capable of sophisticated energy management and substantial improvement in fuel economy.
Probably the single greatest obstacle to utilization of flywheel energy storage has been the lack of a suitable transmission. In order to match the speeds of a spinning flywheel to those of the automobile drive train, a continuously variable transmission with a wide speed ratio range is required.
A number of transmissions have been designed to meet this need but they have been far from perfect in their application to the automobile. An automobile makes certain demands on a transmission, among which are high torque capabilities, efficient power transfer, and long service life. In addition, the control system must be suitable for simple operation. Previous designs have had major drawbacks in one or more of these areas.
Particularly, prior art in continuously variable transmissions have lacked the ability to transfer power efficiently from one shaft to the other and energy lost in the automobile transmission can greatly reduce the performance of the vehicle.
Many of these continuously variable transmissions are of the traction or frictional gearing type in which the speed ratios of an input and an output shaft are varied by moving a roller across the planar face of a disc, where the disc and the roller are separately coupled to an input and an output shaft. Traditionally, the roller is mounted on a shaft for axial movement which also results in radial movement across the face of the disc, thereby changing the speed ratios therebetween.
Such prior art devices are disclosed in U.S. Pat. No. 3,323,384, issued to Wodarka on June 6, 1967; U.S. Pat. No. 3,464,281, issued to Azuma et al on Sept. 2, 1969; U.S. Pat. No. 3,739,658, issued to Scheiter on June 19, 1973; U.S. Pat. No. 3,875,814, issued to Steuer on Apr. 8, 1975; and U.S. Pat. No. 4,137,785, issued to Virlon on Feb. 6, 1979.
These prior art continuously variable transmissions are very low in efficiency and have short service lives because of frictional losses and wear between the various moving parts, especially between the roller and the disc. In particular, many of these devices, in order to avoid slippage between the roller and the disc, overload the contact point therebetween, thereby increasing the friction, resulting in losses of power and excessive wear which can be destructive to both parts. In addition, many of these devices require various gearing mechanisms to control the location of the roller relative to the disc face, thereby also incurring additional frictional losses of power and excessive wear. On the other hand, many of these devices in an attempt to reduce the frictional losses between the roller and the disc reduce the contact pressure therebetween, which, unfortunately, oftentimes leads to excessive slipping between the roller and the disc. Such slippage reduces the transmission of power through the transmission and ultimately results in low efficiency. In addition, many of these devices are capable of transmitting power in only one direction so they are not totally suitable to use in hybrid energy-storage vehicles.